Synthesis And Adsorption Properties Of Modified Biochars For Pb²⁺ Removal

Recently,more and more attention has been paid to the research of biochar.As an important method to produce biochar,Pyrolysis characterizes relatively simple operation,simplified reaction conditions and a wide range of raw materials.In this paper,biochars were prepared adopting pyrolysis method using the biomass of willow and peanut shell as raw materials and activated by CaCl2,KMnO4 modifier pre-impregnation treatment of biomass raw materials and lye processing of raw bio-charcoal method.After that,the effects of modification on bio-carbon structure and the properties of adsorption of Pb²⁺ were investigated.The main research contents are as follows:1.Synthesis and adsorption properties of CaCl2-modified biochars for Pb²⁺removal.The primary biochars FMC,PSC and modified biochars Ca-FMC,Ca-PSC were prepared at 300? using the biomass of willow and peanut shell as raw materials.Then the modification effect of biocar structure and the properties of adsorption of Pb²⁺ were investigated.The results indicate:?1?The ash content,the number of basic groups,the specific surface area and the degree of aromatization of Ca-FMC and Ca-PSC increased while the polarity decreased.And both Ca-FMC and Ca-PSC are amorphous carbon,which has dispersed CaCO3 particles in the structure;?2?The adsorption rate of modified biochar to Pb²⁺was significantly higher than that of unmodified biochar,which showed that the modification significantly enhanced the adsorption of Pb²⁺;?3?The adsorption of Ca-FMC and Ca-PSC on the Pb²⁺ could be well fitted by the pseudo-second-order equation and the adsorption rate constants were 0.01 and 0.03 g·mg-1·h-1 at 25? when pH was 5.5;?4?The adsorption of Ca-FMC and Ca-PSC on the Pb²⁺were in accord with Langmuir isotherm adsorption model and the saturated adsorption amount were 54.32 and 32.80 mg·g-1 at 25? when pH was 5.5.2.Synthesis and adsorption properties of KMnO4-modified biochars for Pb²⁺ removal.The primary biochars and modified biochars were prepared at 300? using the biomass of willow and peanut shell as raw materials.Then the modification effect of biocar structure and the properties of adsorption of Pb²⁺ were investigated.The results indicate:?1?The ash content,the number of basic groups,the specific surface area and the degree of aromatizationof modified biochars increased while the polarity decreased.And MnOX nanoparticles were loaded on the surface of modified biochars;?2?The adsorption rate of Mn-FMC and Mn-PSC to Pb²⁺ was 99% when pH was 5.5,which was significantly higher than that of FMC and PSC,indicating that modification significantly improved the adsorption performance of FMC and PSC;?3?The adsorption of modified biochars on the Pb²⁺ could be well fitted by the pseudo-second-order equation and the adsorption rate constants were 5.89 and 0.77 g·mg-1·h-1;?4?The adsorption of modified biochars on the Pb²⁺ were in accord with Langmuir isotherm adsorption model and the saturated adsorption amount were 150.38 and 208.33 mg·g-1.3.The effect of alkaline post-treatment on adsorption of Pb²⁺ by biocarsThe raw biochar FMC was prepared at 300? using the biomass of willow and then alkaline modified biochar Ly-FMC was obtained by post-treatment FMC.After that,the effect of alkaline post-treatment on adsorption of Pb²⁺ by biocars were investigated.The results indicate:?1?The removal rate of Pb²⁺ by FMC after treatment with 0.5 mol·L-1 lye was increased from 13% to not less than 98%,which indicated that alkali treatment could greatly improve the adsorption effect of FMC on Pb²⁺,and the optimum treatment conditions can be determined as the concentration of alkali is 0.5 mol·L-1 at room temperature;?2?The surface groups of FMC and Ly-FMC were similar,but the number of Ly-FMC was higher.After adsorption of Pb²⁺,the peak intensity of both was weakened and the Ly-FMC was weakened more,which indicated that Ly-FMC has stronger adsorption capacity to Pb²⁺ whose surface contains more ion exchange sites and cation-? adsorption sites;?3?With the increased of pH,the adsorption rate of both to Pb²⁺ increased at the pH value of 2-6.5,and Ly-FMC could maintain a high adsorption rate over a wide pH range;?4?The adsorption of FMC and Ly-FMC on the Pb²⁺ could be well fitted by the pseudo-second-order equation.The adsorption rate constants were 1.71 and 0.95 g·mg-1·h-1 and the equilibrium adsorption amount were 5.89 and 49.83 mg·g-1;?5?The adsorption of FMC and Ly-FMC on the Pb²⁺ were in accord with Langmuir isotherm adsorption model and with the increase of temperature,the equilibrium adsorption capacity decreased.At different temperatures,the RL values were between 0-1,which indicated that the adsorption process was exothermic and favorable.